Signal-receiving circuits



MMYA QQ April 2 @929.

F. A. KOLSTER SIGNAL RECEIVING CIRCUITS Fil'ed June 2 1926 R. m w m Patented Apr. 2 1929.

UNITED STATES PATENT OFFICE.

FREDERICK A. IKOLSTER, OF IALO ALTO, CALIFORNIA, ASSIGNOB. TO FEDERAL TELE- GRAPH COMPANY, 01'! SAN FRANCISCO, CALIFORNIA, A CORPORATION OF CALI- IORNILA.

SIGNAL-RECEIVING CIRCUITS.

Application filed June 24,

My invention relates broadly to high frequency electron tube amplification circuits and more particularly to a high frequency amplification system having means for pre- 5 venting the setting up of undesired oscillations in the electron tube circuits of the amplification system.

One of the objects of my invention is to provide a system of multi-stage electron tube radio frequency amplification where means are connected in the successive circuits of the amplification system fonpreventing the flow back of energy with the inherent generation of oscillations in the high frequency amplification system.

Still another object of my invention is to provide a high frequency amplification system including a plurality of electron tubes Where means are inserted in the grid cir-' cuits of each of the electron tubes for preventing the fiow back of interfering energy in, the successive tube circuits while permitting the increase in amplitude of the high frequency signaling energy through the successive stages of amplification without interference.

Still another object of my invention is to provide a high frequency electron tube amplification system comprising a plurality of electron tubes coupled successively one to another with means connected in the grid leads of each of the amplification stages offering a high apparent resistance to currents at the shortest wave length to be re- 0 ceived which automatically reduces in value as the received wave length increases for preventing the undesired generation of oscillations in the amplification circuits.

Another object of my invention is to provide a circuit arrangement for an electron tube amplification system where a pair of parallel branch circuits are inserted in thegrid leads of successive electron tubes, one branch circuit including inductance and capacity in series and the other branch circuit containing substantially pure resistance arranged in such relation that the impedance of the circuit varies with "frequency for preventing the setting up of undesired oscillations in the receiving circuits.

1926. Serial No. 118,245.

Other and further objects of my invention will be understood from the specification hereinafter following by reference to the accompanying drawings which diagrammatically illustrate a radio frequency amplification system embodying the principles of my invention.

In a radio frequency amplifier system including a plurality of electron tubes with input and output circuits successively coupled one to another there is a tendency for amplified energy in'one electron tube circuit to partially feed back to a preceding electron tube circuit by virtue of the inherent capacity and resistance existing between the electrodes of the electron tubes, as for example between the plate and grid electrodes. This energy flow back causes undesired oscillations particularly at shorter wave lengths.

Attempts have been made to overcome these undesirable effects by neutralizing or balancing out methods, but the circuits employed are relatively complicated and diificult to assemble in quantity production of radio receiving apparatus. By my invention, however, I provide a method which prevents rather than neutralizes the flow back of energy by inserting in the grid leads of the successive stages of electron tube amplification a parallel circuit, one portion of which consists of inductance and capacity and the other portion of which consists of substantially pure resistance. The constants of the circuit, that is the value of S5 inductance, capacity and resistance are so proportioned and chosen as to give at the shortest wave length to be received a high apparent resistance which automatically reduces in value as the received wave length increases.

Referring to the drawings in detail, reference characters 1, 2 and 3 represent electron tubes having grid, filament and plate electrodes arranged in the successive stages 5 of a radio frequency amplification system. Each of the electron tubes is provided with input and output circuits interconnecting the grid, filament and plate electrodes. The input circuit of the radio frequency amplibranch of which contains resistance R. The

output circuit of electron tube 1 includes primary winding 10 of the high frequency transformer 11 having a secondary winding 12 coupled with the primary winding 10 and connected in the input circuit of the succeeding electron .tube 2 forming the second stage of radio frequency amplification. The auxiliary circuit of my invention is represented at 14: connected in the grid lead of electron tube 2 and including the aforementioned parallel branch circuits having inductance, capacity and resistance arranged as shown. The output circuit of electron tube 2 contains primary winding 15 of high frequency transformer 16 with secondary winding 17 coupled to the winding 15 and connected in the input circuit of the electron tube 3 in series with the auxiliary circuit 18. The auxiliary circuit 18 includes parallel branch circuits having inductance, capacity and resistance elements arranged as indicated. The output circuit'of the electron tube 3 contains the primary winding 19 of high frequency transformer 20 having secondary winding 21 from which extend connections to any desired number of succeeding stages of amplification or to a detector system.

I have represented the several stages of amplification as having independent A and B battery systems for the purpose of more clearly explaining the invention, but it will be understood that the usual circuit arrangement may be provided for supplying space current and filament heating current from a common source.

The circuit L, C,-R,'therefore, inserted in the grid lead has the desired characteristic of introducing a high resistance or impedance in the grid lead for short waves gradually and automatically reducing its value of resistance or impedance as the wave length is increased. The successive amplifier circuits are variably tuned to the wavelength which it is desired to receive while the circuit L, C, R, remains fixed. The impedance of .the circuit L, G, R, varies with the frequency. The rate of change of this impedance can be controlled by proper choice of values L and C, and if desired the impeiynee of the circuit can be brought substantlally to zero at the lowest frequency or longest wave length to be received by choosing L and Csuch as to make 1LC =0 at this longest wave length, where L=value of inductance of coil L C=value of capacity of condenser C I have described and illustrated my invention in one of its preferred embodiments, but I desire it to be understood that modifications in detail may be made and that no limitations upon my invention are intended other than are imposed by the scope of the appended claims.

What I claim as new and desire to secure by Letters Patent of the United States is as follows:

1. A signal receiving system including a "plurality of electron tubes each having grid,

filament and plate electrodes, input and output circuits interconnecting said electrodes with the output circuit of one electron tube interlinked with the input circuit of a succeeding electron tube, and a pair of parallel branch circuits connected in the input circuits of said electron tubes, an inductance and capacity in series in one branch thereof and resistance in the otherbranch thereof, said circuits having an effective resistance variable at a predetermined rate in proportion to the selected signaling frequency for preventing the flow back of undesired oscillatory currents while permitting the free transfer of signaling energy of a selected frequency through said plurality of electron tubes.

2. In a signal receiving system the combination of a plurality of electron tubes each having grid, filament and plate electrodes, input and output circuits interconnecting said electrodes, the output circuit of one electron tube interlinked with the input circuit of a succeeding electron tube, means for se lectivelytuning said input circuits to a desired signaling frequency and means connected in series with each of said input circuits comprising a pair of circuitsconnected in shunt one to the other, one circuit including a capacity and an inductance element in series and adjusted to a frequency outside of the frequency limits for which said circuits are tuned to respond and the other circuit including a resistance element, said capacity inductance .and resistance elements constituting a high impedance in said input circuits for high frequencies and being arranged. to gradually and automatically reduce the value of said impedance as the circuits to a desired signaling frequency and a tuned circuit having a pair of parallel branches connected between said variable means and the grid electrodes of said electron tubes, one of said parallel branches including inductance and capacity in series relationship and the other of said parallel branches including a resistance, the constants thereof being selected to give at the shortest signaling wave length. to bereceived a high apparent resistance which automatically reduces in value to substantially zero impedance at the longest wave length to be received;

In testimony whereof I affix my signature.

FREDERICK A. KOLSTER. 

